a boy goes from his home to school at 10 km per hour and returns at 15 km per hour. find the average speed for the entire journey.

for some reason, the answer key says the answer is 12km/hr. can someone explain why? i feel like there's some missing info in the problem

Question

a boy goes from his home to school at 10 km per hour and returns at 15 km per hour. find the average speed for the entire journey.

for some reason, the answer key says the answer is 12km/hr. can someone explain why? i feel like there's some missing info in the problem

anonymous · Answer

Average Speed = Total Distance / Total Time
The questions is lacking how many hours the boy spent on the road.